1. Field of the Invention
The present invention relates to torque coupling arrangements between two axially adjacent rotatable assemblies that both rotate about a collinear axis and, as shown in the instant embodiments, the present invention also relates to the attachment of a vehicle wheel to its mount frame, more specifically the attachment of a driven bicycle wheel to the driving assembly in conjunction with the attachment to the frame.
2. Discussion of Prior Art
Heretofore, the complete rear drive sprocket assembly is assembled to remain affixed to the rear wheel hub. Thus the rear drive sprocket or sprockets remain attached to the rear wheel when the rear wheel is removed from the frame. Whenever the wheel or tire is damaged, or when the bicycle must be taken apart for service or transport, the wheel, along with its drive sprocket assembly, must be removed from the frame. Such an operation is likely to be required frequently.
Since the drive chain remains with the bicycle frame when the wheel is removed, it is no longer under the tension normally supplied by the wheel sprocket. The chain now tends to dangle and drag on the ground, picking up contaminants and spreading grease onto the surfaces that it comes in contact with. The lack of chain tension also invariably causes the chain to fall off of the front sprockets as well and become tangled.
Reassembly of the wheel to the frame is also problematic, requiring a great degree of skill and dexterity. As the wheel is installed and assembled to the bicycle frame, the operator must insure that the drive chain is properly guided through a series of sprockets and pulleys associated with the rear sprockets, the front chainwheel and the rear derailleur. Further, the present state of the art involves a rear sprocket assembly with as many as eleven sprockets, each selectable via the rear derailleur. Upon reassembly of the rear wheel, the operator must insure that the derailleur is set to the outermost sprocket and that the chain is wrapped around this specific sprocket and also insure that the chain has not inadvertently become disengaged from any of the other sprockets in the drivetrain. This is often a daunting and messy task for most cyclists. While removal of the bicycle's front wheel is a relatively easy operation that may be contemplated by the novice cyclist, removal of the rear wheel is considered to be an intimidating procedure better left to the professional or to an enthusiast fluent in the mechanics of the bicycle.
Further, in a bicycle race, every second is are precious. When the wheel is then reassembled onto the frame, after the repair of a flat tire for instance, the chain will likely now be engaged with the incorrect sprocket for the given conditions as required by the racer. The racer must now waste further time to select the desired sprocket ratio.
In conventional bicycle rear hub designs, the rear wheel sprockets are commonly mounted to the rear hub through a “freewheel” subassembly, where the sprockets are pre-assembled to a one-way rotational clutch mechanism, which is then threaded onto a collar of the rear hub shell. The current state of the art involves a variation on this design and is termed a “freehub”, where the one-way clutch assembly has a splined outer shell that is semi-permanently assembled to the rear hub. This type of clutch subassembly in commonly referred to as a freehub body. The individual sprockets are then slid over this splined shell to receive the bicycle chain. Further description will focus on the freehub type of arrangement although the present invention is easily adaptable to the freewheel configuration or to any other arrangement with similar function, including a sprocket assembly or other power transmission assembly that is rotationally locked to the hub without a one-way clutch.
It should be recognized firstly that the freehub body must be coupled to the hub shell to transmit torque to the rear hub and secondly that the rear hub is mounted to the frame at the two exposed ends of its stationary axle. In these conventional prior art designs, the freehub body (i.e. driving portion of the hub assembly) is fixedly coupled to the hub shell (i.e. driven portion of the hub assembly). In other words, the freehub body and hub shell remain fixed to each other during use and during removal of the wheel from the bicycle frame. Thus, the wheel is commonly assembled to the bicycle frame in a generally radial direction with the axle ends residing in slots within the flattened portions of the frame commonly referred to as “dropouts”. These dropouts generally have a fixed distance of separation, leaving a predefined axial width assigned to the rear hub.
In the past, there have been some novel designs that provide a means to selectively decouple the freehub assembly from the hub shell. In other words, the freehub body (i.e. driving portion of the hub assembly) may be selectively disconnected from the hub shell (i.e. driven portion of the hub assembly). Thus, when the wheel is removed from the frame, the rear hub assembly may be split in two, with the freehub body and its associated drive sprockets, remaining attached to the frame. With the hub shell now disconnected from the freehub body, the entire wheel assembly may be removed from the frame. This type of hub assembly may be termed a “decoupling hub”.
Such decoupling hubs fall into two general categories: the fixed-width type and the telescoping-width type. With fixed-width arrangements, both the driving and driven elements have a fixed axial width. Most decoupling hub arrangements require some degree of axial interference or overlap between the driving and driven elements in order to transmit torque, most often via a splined or keyed engagement. Fixed-width designs required that the bicycle frame must be flexed and the dropouts spread to accommodate this overlap so that the mating engagement splines between the hub and the drive sprockets become disengaged to facilitate removal of the wheel. Such an arrangement adds difficulty to the procedure of disassembly of the wheel from the frame and leaves the frame vulnerable to overstress in this spreading process. This is particularly true if the axial overlap is excessive and if the interface geometry of the mating elements causes the driving and driven elements to snag and/or interfere with each other during removal and/or installation of the wheel. With such prior art designs, this interface geometry also requires special skills and dexterity on the part of the operator to perform the wheel removal and/or installation process quickly and effectively.
Some examples of a fixed width decoupling hub include the Cinelli Bivalent rear hub, which saw limited use in the 1970's and is no longer available. While such designs are intended to be more user friendly than conventional hubs, this has not been the case, since the dropouts must be spread simultaneous with insertion of the hub. Further, the poor design of the aforementioned mating interface serves to make assembly and removal of the wheel a tedious and frustrating experience.
The telescoping width type of decoupling hub utilizes a separate axially slideable telescoping torque coupling element. In such an arrangement, when the torque coupling is slideably extended from either the driving or driven element, it engages both the freehub body (i.e. the driving element) and the hub shell (i.e. the driven element) for the transmission of torque between the two. In other words, when extended, the slideable torque coupling provides axial interference or overlap between the driving and driven elements in order to transmit torque. Conversely, when the torque coupling element is slideably retracted, the freehub body and the hub shell become disengaged, which allows the hub to be removed from the frame while the freehub body remains fixed to the frame. Some examples of this design are described in U.S. Pat. No. 6,374,975.
This telescoping type of configuration involves relatively high complexity with a multitude of expensive precision components. Furthermore, these slideable components create difficult sealing challenges to function in the harsh environment that bicycles are commonly subject to. It should be noted that, as of this writing, none of these designs have been commercially produced.
Accordingly, it is an objective of the present invention to overcome the forgoing disadvantages and provide an improved torque coupling arrangement, particularly as applied to a bicycle wheel.